Accumulation of Total Phenolics, Total Flavonoids, and Polysaccharides in Leaves of Vegetable Jutes at Various Growth Stages

Objective Accumulation of bioactive compounds in the leaves of vegetable jutes during various growth stages was studied for optimal crop cultivation and harvest.

Method Guimacai No.1 and Guimacai No.2 were used as experimental materials, and okra, Chinese yam and lettuce sold in the market were used as controls. Contents of total phenolics, total flavonoids, and polysaccharides in leaves of the plants at seedling, topping, flowering, and capsule stages were measured. Correlations between the plant growth stages and the target bioactive compounds were analyzed.

Result The contents of the bioactive substances varied in same species at different growth stages. As the vegetables grew, the total phenolics in the two vegetable jutes decreased initially followed by an incline which were significantly higher at the capsule stage than other growth stages that peaked at 4.064 mg·g⁻¹ for Guimacai No.1 and 3.852 mg·g⁻¹ for Guimacai No.2. It was also higher at the seedling stage for Guimacai No.1. The total flavonoids in Guimacai No.1 rose initially then fell with the highest content of 2.755 mg·g⁻¹ at the flowering stage. In contrast, the content in Guimacai No.2 increased continuously with a peak of 4.755 mg·g⁻¹ at the capsule stage that was significantly higher than that at other growth stages. Flavonoids were significantly higher in Guimacai No.2 than in Guimacai No.1 at all growth stages. The polysaccharides in Guimacai No.1 were in a fluctuating upward trend, whereas in Guimacai No.2, declining at first and rising afterward. Guimacai No.1 had polysaccharides significantly 3.175%, and Guimacai No.2 1.240%, higher at the capsule stage than other growth stages. Only at the seedling stage when Gamacai No. 2 showed a higher polysaccharide content than Gammacai No. 1. Both vegetable jutes were significantly higher in the contents of total phenolics and total flavonoids than the references at all growth stages, but significantly lower than okra and Chinese yam, except lettuce at the capsule stage on polysaccharides. Only total flavonoid content of Guimacai No.2 was found significantly positively correlated with the growth stages.

Conclusion It appeared that the leaves of Guimacai No.1 and 2 should be harvested at the capsule stage to maximize the benefit of the accumulated total phenolics, total flavonoids, and polysaccharides.